This invention relates to a method of determining the classification of vehicle tires and especially of vulcanized rubber tires according to the materials used therein and the external dimensions thereof, during the process of manufacturing them, and to a device for practising the method. That is, the method and the device are provided for determining whether or not a tire has a ring-shaped decorative white ribbon in its sidewall and for measuring the inside diameter of a tire.
There are many classifications of vehicle tires. One of the classifications is a so-called "white tire" which has a ring-shaped decorative belt (called as "a white ribbon"), on its sidewall. Tires which have no white ribbons are called as "black tires".
The white ribbon is, in general, provided on a tire by the following method: when the tire is molded, a white rubber compound layer including a white pigment such as titanium oxide or zinc oxide which contains metal having a relatively large atomic number is formed in one sidewall of the tire; and the white rubber compound layer thus formed is covered by a black rubber layer. The tire thus treated is subjected to vulcanization, and then the black rubber layer is removed in order to expose the surface of the white rubber compound layer.
Accordingly, the white tire is the same in appearance as the black tire unless the black rubber layer is removed from the white tire. That is, it is difficult to visually distinguish the white tire from the black tire when the white tire including the white rubber compound layer covered by the black rubber layer has been vulcanized.
In general, in a vulcanization process line, which is one of the process lines for manufacturing tires, vulcanizing prosses for white tires and those for black tires are mixedly provided. Therefore, vulcanized tires to be manufactured as white tires are mixed with vulcanized tires to be manufactured as black tires when they are conveyed out of the valcanization process line. The next process for the vulcanized white tires is different from that for the vulcanized black tires. Accordingly, when those tires have been conveyed out of the vulcanization process line, it is necessary to distinguish the valcanized tires for white tires from those for black tires.
Heretofore, although it is difficult to visually distinguish the valcanized tires for white tires from those for black tires, those two kinds of vulcanized tires have been distinguished from each other by a visual inspection because no method suitable to the distinction has been provided, and the vulcanized tires for white tires thus distinguished from are delivered to the next process for the removal of the black rubber layer.
However, this visual inspector is liable to make a mistake in the classification of the vulcanized tires. That is, the vulcanized tires for manufacturing black tires are often delivered to the process of removing the black rubber layer as a result of which the black tires are seriously damaged.
Furthermore, since the white rubber compound layer is formed in only one of the sidewalls of the white tire, it is necessary to determine which sidewall includes the white rubber compound. This determination has been also conducted by a visual inspection. However, similarly as in the distinction between the white tires and the black tires, it is difficult to visually determine which sidewall includes the white rubber compound layer; therefore, the white tires have often been damaged.